branch: typescript

[samreid]

From phetsims/chipper#1069

@zepumph suggested creating a typescript branch for axon and scenery, so at the moment we decide to enable the typescript build chain for all sims, we can immediately get the benefits in common code.

[samreid]

I wrote a draft of Property, but there are some caveats.

• axon and tandem are combined since they have cross references, so they share a tsconfig at the moment
• the tsconfig doesn't include the tests, since the tests include downstream dependencies
• so I disabled precommit hooks to commit.
• the "typescript" branch of axon should not be used with the other typescript branches, because it is for a common repo. Other typescript repos should not depend on this yet, until we have a process and are at that phase.

[samreid]

New idea about how to temporarily use generic Property in typescript sims without having to turn on the typescript build chain for all sims: generate d.ts files from the axon/typescript branch and check the d.ts files in to master.

Pros:

• Enables type safety/autocomplete/navigate for TypeScript projects
• Does not require changing *.js to *.ts in common code

Cons:

• This makes developing axon/typescript more difficult since you have to generate d.ts and move it to master each time
• CMD+B in Java no longer takes you to the *.js file--it now takes you to the d.ts file. There are other navigation methods, but none of them work quite as well as *.js navigating without the d.ts file.

This may be a good strategy until we enable typescript for all repos, if developers are OK with the tradeoffs in the cons section.

[samreid]

While I was working on phetsims/bending-light#401, I noticed there is a JSDoc annotation for template variables in JavaScript, described here: https://stackoverflow.com/questions/16017627/document-generic-type-parameters-in-jsdoc

When I applied this new JSDoc to Property, TypeScript was able to read and understand it. So that seems like a preferable solution until we approve TypeScript in common code. I tested JavaScript usages in Fourier and they didn't seem disturbed. I'll commit this to master shortly.

[samreid]

I was able to use the same JSDoc template pattern for Emitter, supporting an array of types. It's working really well.

    const e0 = new Emitter<[]>();
    e0.emit(); // ok
    e0.emit( 'testing' ); // bad
    e0.addListener( () => {} ); // ok
    e0.addListener( ( age: number ) => {} ); // bad

    const e1 = new Emitter<[ boolean ]>();
    e1.emit( true ); // ok
    e1.emit( 'hello' ); // bad
    e1.addListener( ( enabled: boolean ) => {} ); // ok
    e1.addListener( ( age: number ) => {} ); // bad

    const e2 = new Emitter<[ string, number ]>();
    e2.emit( 'bye', 7 ); // ok
    e2.emit( 'null' ) // bad
    e2.addListener( ( name: string, age: number ) => {} ); // ok
    e2.addListener( ( name: string, age: number, time: Date ) => {} ); //bad

[samreid]

Branch deleted, closing.